He asked: "How does it give the public confidence in the government's anti-radicalisation and anti-terrorism strategy for the former British soldier James Matthews, who fought alongside our Kurdish allies against ISIS in Syria, to be prosecuted for terrorist offences?"

Mrs Rudd responded: "I understand that there are concerns about the level way in which the government are approaching this.

"No individual from this country can go out and fight with another person's army or terrorist organisation in order perhaps to promote their own way of life.

"We have to be very clear and even-handed about this."

Image copyrightPAImage caption
James Matthews has been charged under anti-terror laws

Since 2015 dozens of British volunteers have fought with the Kurds in Syria and Iraq to help recapture IS-held territory.

Amber Rudd's comments are believed to be the first time the UK government has provided some clarification about the way the Home Office views the legality of their actions.

Speaking to the BBC, Mr Bradshaw said he was "appalled" by the decision to prosecute Mr Matthews.

He said: "It cannot be in the public interest to prosecute, as a terrorist, someone who was supporting our allies, the Kurds - and with UK air support - against ISIS.

"James is clearly not a terrorist and poses no threat to the British public. The justice secretary should intervene in this case before it brings our justice system into disrepute."

Mr Matthews' sister, Abby Stapleton, said her brother was a "brave, principled man".